The present invention relates to a drive unit for an exercising apparatus based on providing a friction resistance based on applied force.
The conventional method of providing resistance in an exercising apparatus is to use weights, flexible lines and pulley wheels. This type of apparatus has an inherent problem due to the inertia of the weights. In a typical exercise routine, because it is necessary to first accelerate the weight, force is required not only to lift the weight but also to accelerate it. Typically, once the weight has been initially accelerated, the user applied force is reduced significantly from its maximum, rising slightly towards the end of the exercise. Consequently, weight based exercising devices apply a relatively large force on the muscle over a relatively narrow range of movement in the exercise and a lesser force for the remainder of the movement.
Researchers have proposed a mechanical model of muscle to predict muscle tension based on input loading or stimulation which consists of a contractile component together with a linear series and parallel elastic component plus linear viscous damper. The damper serves to slow down frequency response of the muscle. The contractile component is considered to have an exponential response to a stimulus rising immediately to a maximum and then decreasing exponentially. The elastic components develop force in response to displacement or stretching of the muscle during which time they store potential energy. It is the elastic components which come into play once the contractile force has decreased significantly. Excitation of the elastic components is not considered as contributing significantly to muscle development whereas loading or stimulation of the contractile component is considered to be what stimulates strength gains. In an initial rapid acceleration of a weight, loading is first primarily on the contractile components of the muscles. However, after velocity has increased and acceleration has reduced sufficiently, loading on the contractile components reduces and the elastic components begin to predominate. The initial high loading and subsequent significant drop in loading characteristic of an inertial system further accentuates reduced loading of the contractile component over all but an initial portion of an exercise by reason of the delayed entry of the elastic component.
Much more effective loading results if the muscles of the user are loaded uniformly throughout the range of movement of the exercise so as to increase loading of the contractile components of the muscles.
One method of providing a uniform force substantially independent of acceleration is to utilize a resistance generation method that has a low mass such as one based on friction. U.S. Pat. No. 3,103,357 issued to Berne discloses an adjustable friction based exercising apparatus which utilizes an inner clutch disk sandwiched between outer disk members and in slipping contact with the latter. Hydraulic pressure is used to change the compression force on the central disk to vary the friction force between the disks.
Another method disclosed by U.S. Pat. No. 4,436,303 issued to McKillip utilizes a pair of disks held together in slipping contact by a corresponding pair of hydraulically operated pistons. The friction force required to make the disks slip over one another is adjusted by selecting the pressure applied by the pistons.
U.S. Pat. No. 3,953,025 issued to Mazman discloses a muscle building exercising device in which a pair of brake pads are pressed against each side of a disk.
Each of the foregoing devices disclose the utilization of friction in exercising apparatus to provide a concentric resistance force in which initially the slipping components are at rest. Since the force required to overcome static friction is larger than that required to overcome kinetic friction such devices impose a high threshold loading on the user and a lower load over the remainder of the range of movement of the exercise. Since it is user force which initiates slipping movement, the foregoing devices do not afford the user eccentric resistance in addition to concentric resistance.